1. Field of the Invention
This invention relates generally to seismic surveying and processing of seismic data, and more particularly to combining vertical seismic profiling and reverse seismic data to obtain enhanced seismographs of the earth""s subsurface formations from prior 3D data.
2. Description of the Related Art
The seismic data gathering method referred to as xe2x80x9cvertical seismic profilexe2x80x9d (xe2x80x9cVSPxe2x80x9d) surveys are methods that involve placing seismic wave detectors or receivers at various depths in a well and a seismic source (an acoustic source) at or near the surface. The seismic source is activated or set off at such surface or near surface locations and the signals detected by the sensors are recorded and processed for obtaining subsurface maps for seismographs, which are depth charts of certain geological characteristics of the subsurface formation. In the reverse vertical seismic profile or xe2x80x9cRVSP,xe2x80x9d surveys are methods where data are gathered with receivers placed at spaced-apart locations at the surface in response to an acoustic source activated in a wellbore. Data from VSP and RVSP surveys are processed to obtain and/or enhance seismographs.
Both VSP and RSVP methods have been known in the art. The present invention, however, provides a method wherein the VSP and RVSP surveys are performed by reversing the placements of the seismic sources and receivers and then combining the two (2) sets of data to obtain certain transfer functions, which are then utilized to obtain enhanced seismographs from 3D data.
The present invention provides a method of obtaining and processing seismic data to obtain enhanced geophysical maps from 3D seismic data. A first set of data is obtained from a vertical seismic profile (VSP) survey and a second set from reverse seismic profile survey by reversing the locations of the sources and receivers of the VSP survey. The two sets of data are combined to determine a transfer function or model, which is then applied to a set of 3D seismic data to obtain a seismic map of the area surveyed for the 3D data.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended thereto.